I've done that exact "let's prepend a header" thing before. For a past project, each stage of the build and packaging process resulted in an increasingly-diffic

I've done that exact "let's prepend a header" thing before. For a past project, each stage of the build and packaging process resulted in an increasingly-difficult to use "by hand" file that was increasingly-friendly to downloaders, flashers, and CMS systems. Each system wanted its own file header or format (one, for example, disliked Debian files and insisted that we post a gzipped tarball for some reason). Aside from a stage that encrypted the firmware, if you knew the structures being prepended to the file, you could "undo" all of that with a little bit of perl.